Modern heating and air systems are constructed from steel and flexible ducting that are connected to various plenums, inlets, and outlet fittings. The fittings and plenums are sheet metal structures having a circular hole for receiving a duct collar that is used to connect the flexible ducting to the fitting. The collars must provide a secure, airtight connection between the ducting and the sheet metal. This is particularly important in the systems that use high pressure and/or high velocity air. In addition, starting collars must be inexpensive, both in terms of the cost of the collar and in terms of the installation time needed to install the collar.
The problem of providing a secure, airtight seal is complicated by the fact that the hole in the plenum into which the collar is inserted is often cut in the field, and hence, may vary in size and shape from design specifications. This lack of precision makes it difficult to provide a rigid, secure fitting between the collar and the plenum. In addition, the collar must be sealed with duct tape or caulk to prevent air leakage around the collar. If the collar is not securely attached to the plenum wall, the duct tape seal will eventually fail due to the vibration of the collar induced by airflow through the plenum.
One class of prior art starting collar utilizes tabs to connect the collar to the plenum. These collars require the installer to bend a number of tabs that are cut into the inserting surface of the starting collar to secure the collar to the duct plenum hole. The installer must bend every fourth tab to the outside and the rest to the inside of the cut plenum hole. This type of installation is time consuming. In addition, the seal between the collar and the plenum hole leaks air because the plenum holes typically vary both in size and shape. As a result, the final assembly must be sealed manually with duct tape or caulk. Installation of the duct tape substantially increases the installation time, and hence, the cost of the installation. In addition, the tabs do not provide a secure fit if the hole is too large or oblong in shape. Hence, vibration will, over time, cause the tape seal to fail.
Collar configurations that utilize some form of flange and sheet metal screws for attachment are also known to the art. Once again, to provide an air tight seal, some form of caulking or duct tape must be used to seal the final assembly. In addition, the time needed to screw in several sheet metal screws increases the installation time.
Broadly, it is the object of the present invention to provide an improved collar for making connections between ducting and sheet metal structures.
It is another object of the present invention to provide a collar that provides a tight seal even when the hole to which it mates differs significantly from the design specifications.
It is yet another object of the present invention to provide a collar that provides an airtight seal.
It is still another object of the present invention to provide a collar that can be quickly and easily installed.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
SUMMARY OF THE INVENTION
The present invention is a collar for connecting a duct to a wall having a hole therein bounded by an edge having a predetermined thickness. The collar is constructed from a sheet of material having top, bottom, left and right edges, the sheet forming a tubular structure in which the left and right edges overlap. The sheet includes a groove for engaging the edge of the hole. The sheet also includes first and second detents spaced apart thereon. The overlap of the left and right edges at the top edge changes when the spacing between the first and second detents is changed. The collar also includes a first fastener for fixing the overlap of the left and right edges at the top edge when the edge of the hole is engaged in the groove and a second fastener for fixing the overlap of the left and right edges at the bottom edge. In the preferred embodiment of the present invention, the groove includes a layer of sealing material for forming a seal between the sheet of material and the edge of the hole. The collar is shipped with a removable cover strip over the groove for protecting the layer of sealing material. A ridge for forming a seal with the duct when the duct is installed over the collar may also be included in the sheet.